A papermaker's felt is used in the press section of a papermaking machine to support the paper web as the web is passed through the nip between a pair of cooperating press rolls to extract water from the web.
During endless travel of the felt in the press section of the papermaking machine, the web-supporting surface of the felt is normally passed in direct contact with one or more uhle boxes or suction boxes, and may also ride against supporting rolls, both of which can cause abrasion to the web supporting surface. Additional abrasion can be caused by slippage of the felt, such as slippage between the felt and the paper web, slippage between the felt and rolls, and slippage between two felts. Thus the web carrying surface of the felt must have a certain flexibility and toughness to withstand this abrasive action.
In addition, the felt is subjected to substantial compressive stress as it passes through the nip between the press rolls, and the web supporting surface of the felt must be resistant to the compressive stress to prevent tearing or rupture.
It has been proposed to utilize a polymeric foam material, such as polyurethane foam, as a web-supporting component in a felt. However, the foam layer, if skived to thickness, has an outer web-supporting surface which is too weak to resist abrasion and other dynamic forces to which the felt is exposed in the papermaking process so that the foam material tends to abrade and tear away in large pieces which are detrimental to the paper machine operation.
On the other hand, it is possible to form a polymeric foam layer with a relatively thick and rubbery surface skin, and while a skin of this type is capable of resisting abrasion, it lacks the necessary permeability to be used as a web-supporting surface in a papermaker's felt.